1. Field of the Invention
This invention relates to a method and apparatus for stacking a plurality of individual plates and more precisely an apparatus and method for making a stack of plates having a precise height from a plurality of individual plates having varying thicknesses and uneven distribution of thickness throughout the plates.
2. Description of the Prior Art
There are many diverse arts from battery making to motor and generator making which require the assembly of a plurality of plates or laminates into groups or stacks. Depending on the application, the importance of the tolerances of both the thickness of the individual laminates and the overall height of the finished stack can vary from being unimportant to being very critical. In applications where the laminates are being assembled to build the alternator of a motor, the thickness tolerances of the individual laminates can be relatively large, but the tolerances for the overall stack height are very small.
Because the individual laminates for an alternator do not need precision tolerances, the individual laminates can be manufactured quite inexpensively with tolerances as large as 0.008 inches and with an uneven distribution of thickness throughout the plates. Normally, two different types of laminates are used in building the alternator stator, a thinner smaller diameter laminate having a thickness of one-half millimeter and a slightly thicker, slightly larger diameter laminate having a thickness of one millimeter.
The only previously known method of assembling a plurality of varying thickness laminates into a stack having a precise height was to manually select an appropriate number of laminates and to measure and adjust the total height of the stack such that it would be exactly one inch. In practice it was found that the laminates were manufactured such that the uneven distribution of thickness was generally the same for each laminate. Thus if all of the laminates were assembled in the stack with the same orientation, the overall height of the stack would vary depending upon the location where the measurement was taken. The stack was usually leveled by simply stacking one-half of the laminates in a first orientation and stacking the remaining laminates in a second orientation rotated 180.degree. from the first orientation.
Obviously, the manual method of producing a stack of laminates that were precisely a certain height was slow, costly and occasionally inaccurate. Any known stacking machines disclosed in the prior art could not be used since they did not provide for producing a stack having a critical height. Many of the prior art devices used for assembling storage battery elements, such as those disclosed in U.S. Pat. Nos. 2,626,038 to Smith, and 2,680,510 to Donath were comprised of a plurality of stations containing a stack of laminates and a means for individually dispensing the laminates on the top of a pile being formed. In the Smith patent, vacuum means pick up the top laminate in the stack and place it on top of a pile of laminates being conveyed past the stations by an endless belt conveyor. In the Donath patent, individual battery plates are released and dropped from the bottom of a dispensing magazine onto an intermittently operated endless belt conveyor. Although the devices disclosed in the battery assembling apparatus could produce a pile of laminates having a precise number of laminates, they were not capable of measuring the height of the pile of laminates and varying the height by adding or subtracting laminates therefrom to produce a pile having a precise height. In addition, assembling apparatus using vacuum means were generally very noisy, expensive, susceptible to frequent breakdowns or to inadvertently dropping a laminate at the wrong location.